Infrared Diode Laser Spectroscopy Research Articles

Infrared spectroscopy of 2ν4 and ν3 + 2ν4 bands of the NO3 radical

The 2ν4 band spectrum of 14NO3 observed with infrared diode laser spectroscopy was analyzed with the Fourier transform (FT) spectrum in the 760cm−1 region, including the Coriolis interaction between v4=2 and v2=1. The vibrational frequencies of v4=2, l=0, and l=±2 have been determined to be 752.4033(86) and 771.7941(81)cm−1, respectively. By considering the anharmonic interaction among the 2ν4, ν3, ν4, ν2, and ν2+3ν4 states, a relation among the cubic anharmonic constants was obtained as 0.452 Φ444ζ2,4−0.271 Φ344ζ2,3=127.7cm−1. The ratio of transition moments μ(ν2)/μ(2ν4) was determined to be 0.3 from the perturbation analysis. The second strongest infrared band of 14NO3, ν3+2ν4, observed around 1927cm−1has been analyzed with the hot band ν3+2ν4−ν4 by including the Coriolis interaction with the v2=1, v4=3 state. Similarly, the same band of 15NO3 was analyzed to give the band origin of 1897.9325(6)cm−1. The isotope shift 28.2cm−1 for the ν3+2ν4 vibrational frequency is consistent with a predicted value of 27.3cm−1. Although there are two A′ states in v3=1, v4=2, only one A2′ state has been assigned in the hot band, indicating that the other band has weak intensity. This fact and the strong intensity of the ν3+2ν4 band (l3=±1, l4=0) are understood as the effect of vibronic interaction. The first-order Coriolis coupling constant ζ of ν3+2ν4, l3=1, l4=0 is similar to those of the ν4 and ν3+ν4 states, and it is concluded that the vibrational Coriolis coupling constant is nearly zero and the observed constants of ζ=−0.19 (14NO3) and ζ=−0.15 (15NO3) also originate from the effect of vibronic interaction.

Product Channels in the Reaction of the Hydroxymethyl Radical with Nitric Oxide.

The products of the reaction of CH2OH with NO were studied by infrared diode laser spectroscopy. Products were detected to determine the branching ratios of the CH2OH + NO reaction. HNCO was detected in 10.3 ± 2% yields. No other products were detected in significant quantities, indicating that adduct formation is the primary reaction pathway. Ab initio calculations of the potential energy surface show a low energy pathway to HNCO + H2O, but no other bimolecular channels, in agreement with the experiments.

Infrared diode laser spectroscopy of H2O–CO2 and D2O–CO2 complexes in the v2 bend region of water

The rovibrational spectrum of H2O–CO2 and D2O–CO2 weakly bound complexes has been measured in the v2 bend region of the water monomer by infrared diode laser absorption spectroscopy. Rotational and centrifugal distortion constants for different internal rotation states in the excited vibrational state have been determined. The band-origin of the spectrum is blue-shifted from that of the water monomer by 0.739cm−1 for H2O–CO2 and 0.083cm−1 for D2O–CO2, respectively. The tunneling splitting is reduced upon vibrational excitation by 0.00698(31)cm−1 for H2O–CO2 and 0.00044(17)cm−1 for D2O–CO2, respectively.

Investigations on the active screen plasma nitriding process

This study presents the mechanism of nitrogen transfer in a large scale active screen plasma nitriding (ASPN) unit. The active screen provides a homogeneous temperature distribution within the workload as well as an arcing tendency is reduced, since the plasma is moved from the treated work pieces to the active screen. In order to study the mechanisms in detail, plasma diagnostics is necessary. The applied diagnostic methods for analyses of the excited process gas synthesised by the active screen include mass spectrometry and infrared diode laser spectroscopy (TDLAS). Together with a metallurgical characterisation of nitrided steels a better understanding of the chemical phenomena in the N2-H2 plasmas is achieved. Various N2/H2 gas mixtures and variable bias activation powers at the pressure of 200 Pa were investigated. It was found that even during heating up in nitrogen free process gas exited nitrogen (atomic or molecular) releases from the active screen. Infrared diode laser spectroscopy has been used as a diagnostic methode to measure the concentrations of the stable NH3 molecules downstream the plasma source. The ammonia production turns out to depend on the mixtures of N2-H2 and the current input of the bias activation. The results are discussed with the plasma parameters measured by the electrostatic probe. Thus, a contribution to the interpretation of the mass transfer in ASPN process has been realised.

Infrared diode laser study of the kinetics of the NCCO + O 2 reaction

Infrared diode laser spectroscopy was used to probe the kinetics of the NCCO + O 2 reaction. Several NCCO transitions were detected at 1887–1890 cm −1, in good agreement with a recent high-level calculation for the ν 2 fundamental vibrational frequency. The total rate constant of the NCCO + O 2 reaction was measured to be (5.2 ± 0.5) × 10 −13 cm 3 molecule −1 s −1 at 2 Torr pressure of N 2. The NCO + CO 2 product channel was detected for the first time by probing 18OC 16O products from NCCO + 18 O 2 . The branching ratio for this channel was estimated to be 0.28 ± 0.06 at 3.2 Torr total pressure.

Measurement and analysis of rotational lines in the (2ν1+ν2+ν3) overtone band of H2O perturbed by CO2 using near infrared diode laser spectroscopy

Abstract We report the CO 2 -induced broadening coefficients and line strength parameters of water vapor rovibrational transitions belonging to the (2 ν 1 + ν 2 + ν 3 ) overtone band measured by using an NIR diode laser spectrometer. Rotational quantum number dependence of the broadening coefficients is also shown. Use of balanced photodetector and wavelength modulation spectroscopy with small current modulation amplitude helped to obtain improved S / N ratio of the spectra. The recorded line shapes are fitted with standard Voigt profile by using a non-linear least squares fitting program to extract the line shape parameters.

Cross Determination of the Vapor Liquid Equilibrium of Formaldehyde Aqueous Solutions by Quadrupole Mass Spectrometry and Infrared Diode Laser Spectroscopy

Quantitative measurements of the partial vapor pressure of formaldehyde are performed above aqueous H2CO solutions of different concentrations (from 10(-5) to 0.3 molar fraction) using mass spectrometry and IR diode laser spectroscopy. Both experimental techniques allow direct probing of the gas phase concentration collected at equilibrium above the aqueous solutions. A correlation is observed between the polymerization processes occurring in the solution and the partial pressure of H2CO measured at vapor liquid equilibrium (VLE). A similar correlation is observed from total pressure measurements for which the equilibrium vapor pressure decreases as [VLE XH2CO]liq is increased. A saturation regime of the H2CO partial pressure is reached as the dissolved fraction of formaldehyde increases above approximately 0.15 mol frac. Henry's law constants are derived at 295K for the diluted solutions.

Near infrared laser spectroscopy of solid parahydrogen: The crystal-field splitting of rovibrational W1(0) transition

The fine structure of the rovibrational W 1(0) transition ( v = 1 ← 0, J = 6 ← 0) of solid parahydrogen has been observed using high-resolution near infrared diode laser spectroscopy. Similar to the case of the pure rotational W 0(0) transition, the W 1(0) transition also exhibits triplet structure which is interpreted as the crystal-field split M components of the J = 6 manifold. The observed splitting is consistent with the theoretical prediction based on the localized J = 6 rotons. The crystal-field splitting parameters obtained by least-squares fitting are in good agreement with the previous work on W 0(0) transition.

Time-resolved infrared diode laser spectroscopy of the ν1 (C–O stretch) band of the CoCO radical

Infrared spectrum of the cobalt carbonyl radical CoCO produced by the 193 nm excimer laser photolysis of cobalt tricarbonyl nitrosyl Co(CO) 3NO was observed by time-resolved diode laser spectroscopy. More than 600 lines were identified as belonging to the ν 1 (C–O stretch) fundamental band, consisting of the Ω = 5 / 2 and 3/2 subbands, and the associated hot bands 1 1 2 , 1 0 1 2 1 1 , 1 0 1 3 1 1 , and 1 0 1 2 2 2 . The 2 Δ i electronic ground state of CoCO was experimentally confirmed. The ν 1 band origins are 1974.172582(93) cm −1 and 1973.53178(14) cm −1 for the Ω = 5 / 2 and 3/2 subbands, respectively. The rotational constant in the ground state was determined as B 0 = 4427.146 ( 50 ) MHz. The centrifugal distortion constant D 0 = 1.1243 ( 68 ) kHz was obtained for the Ω = 5 / 2 substate of the ground state. The equilibrium rotational constant B e = 4435.44 ( 14 ) MHz was derived, together with the vibration–rotation interaction constants.

Formaldehyde measurements in libraries: Comparison between infrared diode laser spectroscopy and a DNPH-derivatization method

Formaldehyde concentrations have been measured in the university libraries in Strasbourg (east of France). Infrared diode laser spectroscopy and a conventional DNPH-derivatization method followed by liquid chromatography coupled to UV detection have been used simultaneously for comparison purposes. The formaldehyde concentrations obtained by both the techniques were always in excellent agreement, showing that the infrared diode laser spectroscopy can be used for formaldehyde monitoring in indoor atmosphere, with a time resolution of few minutes. Formaldehyde concentrations were generally found to be in the range 8–33 μg m −3, except for two libraries where concentrations of 82 and 105 μg m −3 have been measured. Using the results obtained by both techniques, the resulting mean formaldehyde level in the investigated libraries was then 33.5±31.2 μg m −3, where the quoted error correspond to the standard deviation. Acetaldehyde and hexanal levels have also been quantified by duplicated measurements in the same libraries by the DNHP-derivatization method. They ranged from 0.0 to 11.3 μg m −3 for acetaldehyde and from 1.0 to 16.7 μg m −3 for hexanal and their mean values were found to be 2.1±3.2 μg m −3 (acetaldehyde) and 4.0±4.4 μg m −3 (hexanal), where the quoted errors correspond to the standard deviation.

Infrared diode laser spectroscopy of jet-cooled NiCO, Ni(CO)3(C13O), and Ni(CO)3(CO18)

Gas phase infrared spectroscopic investigations of the CO vibration of jet-cooled NiCO, Ni(CO)3(13CO), and Ni(CO)3(C18O) are reported. The spectra were obtained using a recently assembled pulsed-discharge slit-jet IR diode laser spectrometer. The rotationally resolved spectrum of NiCO was collected as it was formed in the discharge, while the spectra of Ni(CO)3(13CO) and Ni(CO)3(C18O) were recorded as they were destroyed. For NiCO, band origins of 2010.692 89(34) and 2010.645 28(23) cm(-1) were measured, along with values of B0=0.151 094(7) and 0.149 597(6) cm(-1) and B(1)=0.150 244(7) and 0.148 742(6) cm(-1) for 58NiCO and 60NiCO, respectively. The B0 values for these isotopologs were used to determine the two bond lengths in NiCO, giving r0 (Ni-C)=1.641(40) A and r0 (C-O)=1.193(53) A, in agreement with recent microwave measurements. The constants determined for Ni(CO)3(13CO) were upsilon0=2022.075 753(95) cm(-1), B"=0.034 736(2) cm(-1), and B'=0.034 688(2) cm(-1). For Ni(CO)3(C18O), upsilon0=2021.936 83(18) cm(-1), B"=0.033 764(4) cm(-1), and B'=0.033 710(4) cm(-1) were obtained. From these rotational constants, bond lengths of r0 (Ni-C)=1.839+/-0.007 A and r0 (C-O)=1.121+/-0.010 A were obtained. These values are discussed in relation to the bond lengths measured by electron and x-ray diffraction methods.

Infrared diode laser spectroscopy of the △ ν = 2 band of AlF

A vibrational–rotational spectrum of the △ ν = 2 transitions of a high-temperature molecule AlF was observed between 1490 and 1586 cm −1 with a diode laser spectrometer. Measurements were made on the ν = 3–1, 4–2, 5–3 and 8–6 bands at a temperature of 900 °C. Measured spectral lines were fitted to effective band constants ν 0, B ν and D ν for each band. Present measurements were made with only one Pb-salt laser diode. Physical significance of the effective band constants is discussed.

A Kinetic and Product Study of the Cl + HO2 Reaction

Absolute rate data and product branching ratios for the reactions Cl + HO2 --> HCl + O2 (k1a) and Cl + HO2 --> OH + ClO (k1b) have been measured from 226 to 336 K at a total pressure of 1 Torr of helium using the discharge flow resonance fluorescence technique coupled with infrared diode laser spectroscopy. For kinetic measurements, pseudo-first-order conditions were used with both reagents in excess in separate experiments. HO2 was produced by two methods: through the termolecular reaction of H atoms with O2 and also by the reaction of F atoms with H2O2. Cl atoms were produced by a microwave discharge of Cl2 in He. HO2 radicals were converted to OH radicals prior to detection by resonance fluorescence at 308 nm. Cl atoms were detected directly at 138 nm also by resonance fluorescence. Measurement of the consumption of HO2 in excess Cl yielded k1a and measurement of the consumption of Cl in excess HO2 yielded the total rate coefficient, k1. Values of k1a and k1 derived from kinetic experiments expressed in Arrhenius form are (1.6 +/- 0.2) x 10(-11) exp[(249 +/- 34)/T] and (2.8 +/- 0.1) x 10(-11) exp[(123 +/- 15)/T] cm3 molecule(-1) s(-1), respectively. As the expression for k1 is only weakly temperature dependent, we report a temperature-independent value of k1 = (4.5 +/- 0.4) x 10(-11) cm3 molecule(-1) s(-1). Additionally, an Arrhenius expression for k1b can also be derived: k1b = (7.7 +/- 0.8) x 10(-11) exp[-(708 +/- 29)/T] cm3 molecule(-1) s(-1). These expressions for k1a and k1b are valid for 226 K < or = T < or = 336 and 256 K < or = T < or = 296 K, respectively. The cited errors are at the level of a single standard deviation. For the product measurements, an excess of Cl was added to known concentrations of HO2 and the reaction was allowed to reach completion. HCl product concentrations were determined by IR absorption yielding the ratio k1a/k1 over the temperature range 236 K < or = T < or = 296 K. OH product concentrations were determined by resonance fluorescence giving rise to the ratio k1b/k1 over the temperature range 226 K < or = T < or = 336 K. Both of these ratios were subsequently converted to absolute numbers. Values of k1a and k1b from the product experiments expressed in Arrhenius form are (1.5 +/- 0.1) x 10(-11) exp[(222 +/- 17)/T] and (10.6 +/- 1.5) x 10(-11) exp[-(733 +/- 41)/T] cm3 molecule(-1) s(-1), respectively. These expressions for k1a and k1b are valid for 256 K < or = T < or = 296 and 226 K < or = T < or = 336 K, respectively. A combination of the kinetic and product data results in the following Arrhenius expressions for k1a and k1b of (1.4 +/- 0.3) x 10(-11) exp[(269 +/- 58)/T] and (12.7 +/- 4.1) x 10(-11) exp[-(801 +/- 94)/T] cm3 molecule(-1) s(-1), respectively. Numerical simulations were used to check for interferences from secondary chemistry in both the kinetic and product experiments and also to quantify the losses incurred during the conversion process HO2 --> OH for detection purposes.

Study of an H2/CH4 moderate pressure microwave plasma used for diamond deposition: modelling and IR tuneable diode laser diagnostic

Infra-red tuneable diode laser spectroscopy (IR TDLAS) has been used to detect and quantify the methyl radical and three stable carbon-containing species (CH4, C2H2 and C2H6) in a moderate pressure microwave (f = 2.45 GHz) bell-jar reactor used for diamond films deposition. A wide range of experimental conditions was investigated, with typical pressure/power required to perform diamond deposition, i.e. pressure from 2500 to 12 000 Pa and power from 600 W to 2 kW, which means gas temperatures ranging from 2200 to 3200 K, when the power density increases from 9 to 30 W cm−3. Since TDLAS is a line of sight averaged technique, the analysis of the experimental data required the use of a one-dimensional non-equilibrium transport model that provides species density and gas temperature variations along the optical beam. This model describes the plasma in terms of 28 species/131 reactions reactive flow. The thermal non-equilibrium is described by distinguishing a first energy mode for the electron and a second one for the heavy species. Parametric studies as a function of power density and methane percentage in the gas mixture are presented. The good agreement obtained between measurement and one-dimensional radial calculations allows a validation of the thermo-chemical model, which can be used as a tool to enlighten the chemistry in the spatially non-uniform H2/CH4 microwave discharge used for diamond deposition. This is especially of interest for high power density discharge conditions that remain poorly understood.

Near infrared diode laser cw slit jet investigations of O13C:HCl, 14N2:HBr and OC:HBr

Application of near infrared diode laser spectroscopy for enhanced investigation of neutral closed shell molecular complexes is reported. The capabilities of high-frequency wavelength modulation with second derivative absorption detection using a cw supersonic slit jet expansion are demonstrated by an investigation of the previously unrecorded ν1 K=2←1 P1(J) and P2(J) transitions of OC:Ar with transitions having signal-to-noise ratios up to 103:1. Subsequently, rovibrational analyses are reported for the hydrogen-bonded interactions: (i) ν1 O13C–H35Cl and O13C–H37Cl in natural abundance; (ii) analysis of a Coriolis perturbation in J′=19 of ν1 excited state in 14N2–HBr; (iii) ν1, ν2+ν51, ν2+ν51−ν51 in OC–H79Br and OC–H81Br, and generation of rovibrational parameters for the ground-state low frequency intermolecular vibrational ν51.

Near infrared diode laser cw slit jet investigations of O 13C:HCl, 14N 2:HBr and OC:HBr

Application of near infrared diode laser spectroscopy for enhanced investigation of neutral closed shell molecular complexes is reported. The capabilities of high-frequency wavelength modulation with second derivative absorption detection using a cw supersonic slit jet expansion are demonstrated by an investigation of the previously unrecorded ν 1 K=2←1 P 1( J) and P 2( J) transitions of OC:Ar with transitions having signal-to-noise ratios up to 10 3:1. Subsequently, rovibrational analyses are reported for the hydrogen-bonded interactions: (i) ν 1 O 13C–H 35Cl and O 13C–H 37Cl in natural abundance; (ii) analysis of a Coriolis perturbation in J′=19 of ν 1 excited state in 14N 2–HBr; (iii) ν 1, ν 2+ ν 5 1, ν 2+ ν 5 1− ν 5 1 in OC–H 79Br and OC–H 81Br, and generation of rovibrational parameters for the ground-state low frequency intermolecular vibrational ν 5 1.

Isotope analysis of water by means of near infrared dual-wavelength diode laser spectroscopy

A novel diode laser spectrometer was developed using dualwavelength multiplexing, ensuring ideal conditions for high-precision and simultaneous measurements of the 2H/1H, 17O/16O, and 18O/16O isotope ratios in water. A 1.4-m diode laser probed a H16OH / HO2H line pair near 7198 cm-1, while a similar laser observed H16OH, H17OH, and H18OH rovibrational lines around 7183 cm-1, or a H16OH / H18OH line pair near 7200 cm-1. The 1-sigma standard deviation is 0.2 per thousand for 18O/16O, and 0.5 per thousand for the 2H/1H and 17O/16O isotope ratios. Preliminary experiments with repeated injections of a natural abundance sample point to an accuracy of about 1 per thousand for all three isotope ratios in natural samples.

Kinetics of the NCN Radical.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Kinetics of the NCN Radical

The kinetics of the NCN + NO reaction has been studied using laser-induced fluorescence spectroscopy over the temperature range 298−573 K to measure total rate constants and time-resolved infrared diode laser spectroscopy as a probe for possible products. The reaction has a rate constant of k(NCN + NO) = (2.88 ± 0.2) × 10-13 cm3 molecule-1 s-1 at 298 K and low (∼3 Torr) total pressure. The rate constant displays both a temperature as well as a pressure dependence, indicating that adduct formation is a major product channel. Only very small amounts of other products were detected. Upper limits for the low-pressure rate constants of NCN + O2, C2H4, and NO2 were also obtained.

Variable pressure infrared diode laser spectroscopy: a new method for trace-gas monitoring.

A new method for measuring trace concentrations of atmospheric pollutants by infrared diode laser spectroscopy has been devised. This method relies on the increase of the signal as the pressure inside the cell increases, while the frequency of the diode is stabilized on the line, even if it is unresolved. Performances of this method were tested with N2O and with 1,3-butadiene. As an example of application, we measured the butadiene emitted by car exhausts. Sensitivity and rapidity of this method are equivalent to the usual scanning method in which the whole line is described, but this new method benefits from its simplicity and robustness.